1. Field of the Invention
The present invention relates to a resource manager for a multispot or multibeam satellite telecommunication system including user terminals sending data to a plurality of spots each representing the intersection with the surface of the Earth of a satellite beam representing the radiation diagram of an antenna of the satellite. This type of satellite allows the use of a plurality of satellite antenna beams to cover contiguous geographical areas, instead of a single wide beam. The present invention is more particularly suited to systems using a satellite or satellites to provide up to several tens of spots (from around 10 spots to around 100 spots). Such systems hove an increased capacity because of the improved link balance obtained with narrow beams and the facility to reuse frequencies between the beams.
2. Description of the Prior Art
As shown in FIG. 1, a telecommunication system 100 of the above kind includes user terminals 2, 7 in the form of ground stations communicating with each other via a satellite 3 on board which is an onboard switch 11. The onboard switch 11 receives at its input ports uplinked data, i.e. data that is uplinked from the various ground stations 2 to the satellite 3, and distributes from its output ports downlinked data, i.e. data downlinked from the satellite 3 to other ground stations 7. The terminals 2 that send to the same input port of the switch 11 are grouped in the same spot 1. Similarly, the terminals 7 that receive data from the same output port of the switch 11 are grouped into a spot 8. The satellite 3 routes traffic directly between the spots 1 and 8 by means of the onboard switch 11, which minimizes the use of terrestrial networks. The terminals 2 are very often in competition for use of the resources consisting of the uplink and downlink bandwidth of the satellite 3.
Many devices known in the art provide a solution to the problem of dynamic management of the resources of a satellite system authorizing dynamic connectivity between spots via the satellite.
One solution is to use a demand assignment multiple access (DAMA) controller based on a protocol for dynamic assignment of resources and which assigns user terminals frequency and time slots when said terminals express the requirement to send data in the form of packets on uplinks from a terminal to a satellite by sending requests to the DAMA controller. An onboard switch on the satellite then distributes the data packets arriving on a plurality of uplinks to a plurality of downlinks. The onboard switch can be of two types. The first type is a packet switch. It routes each data burst or packet individually as a function of routing information transmitted with the packet itself or in a separate control channel. The second type is a circuit switch. It routes received signals or information as a function of its time and frequency position on the uplink. A circuit switch effects deterministic multiplexing. The time and frequency position of signals or information received on each uplink must therefore conform to the routing configuration of the switch. A packet switch effects statistical multiplexing at each of its outputs. Thus it can happen that many packets have the same output of the switch as their destination: this results in conflict. The conflict is resolved by means of a buffer memory.
However, the buffer memory has a limited capacity. If that capacity is exceeded, a phenomenon known as congestion results.
A first solution to this problem is to increase the size of the buffer memory, but this requires memories of very high capacity, and therefore represents a penalty in terms of mass and power consumption on board a satellite.
The document FR2811841 describes a solution to the above problem.
To this end, it includes a congestion control device which receives requests sent by user terminals from the satellite concerned, each request expressing a requirement to use resources of the satellite; the request combines all the requirements of a given terminal with respect to a given destination spot. This set of requirements is referred to as a virtual path. Virtual paths 4 are shown in FIG. 1 and constitute all of the stream of data from a given terminal 2 to the same destination spot 8. The congestion control device then uses the requests that it receives to determine the resources authorized for each virtual path, taking into account the available resources at the outputs of the switch. The authorized resources are then supplied to a DAMA controller which allocates resources to the user terminals on the uplinks from the terminal to the satellite. The congestion control device therefore takes a preventive approach to congestion.
However, problems arise from its use. Computing authorized bit rates for each request associated with a virtual path leads to a long computation processing time.
Also, the interaction between the congestion control device and the DAMA controller is relatively complex; this is because data is exchanged each time that a request is received from a terminal.
Furthermore, if a new request corresponding to a virtual path is received by the congestion control device, it must be fully satisfied if the capacity of the output of the switch allows this. This approach can give too high a priority to the most recent request because, if the congestion control device authorizes a large quantity of resources in response to a request from a first terminal, the next request from another terminal cannot be fully satisfied unless the first terminal has not sent another request. This phenomenon can lead to unfair distribution of authorized resources.
The present invention aims to provide a resource manager for a satellite telecommunication system which limits the computation processing time and the complexity of exchanges between the congestion controller and the DAMA controller and avoids the unfair distribution of authorized resources.